The prison authorities went to extraordinary lengths to protect the man convicted of killing Martin Luther King from possible assassination, suicide or escape while he was awaiting extradition from Wandsworth prison, papers released yesterday by the public record office reveal.

At the request of the US government, James Earl Ray was placed under 24 hour surveillance and put in a cell where a long range rifle could not be aimed at the window. According to Mark Maunsell, who was inspector general of prisons at the time and was summoned to the American embassy to discuss Ray's security, the US government feared that Ray's associates or enemies would try to kill him or he would try to kill himself.

"The real concern seemed to me to spring from the possibility that there may be people for whom Ray's return to the US in order to give evidence is so alarming that they will proceed to any lengths to kill him while he is in England," Mr Maunsell wrote in a memorandum to the governor of Wandsworth prison.

"In this area the use of a helicopter must not be ruled out," he wrote, emphasising that if a low flying aircraft went near to the prison during exercise Ray should be removed from the yard immediately.

Ray had fled to Europe following the assasination of the black civil rights leader in Memphis in April 1968. After spending three weeks hiding in London he was arrested at Heathrow airport on June 8 travelling under the alias Ramon George Sneyd. He was carrying a revolver with five rounds of ammunition.

Fred Vinson, the assistant US attorney general, told Mr Maunsell how concerned he was that Ray should be safely returned to the US. "This was solely due to the awful consequences within the US if anything intervened," Mr Maunsell wrote. "He [Vinson] said that his government knew, from the president downwards, that nothing would persuade the American public of the validity of the reasons given for any failure, and that disorders would unquestionably follow. They have no means of knowing whether and if so how he, his associates or his enemies might seek to secure his death or escape."

Mr Vinson warned that Ray was an expert in escape from prison, having successfully absconded from the Missouri state penitentiary on July 10 1967, where he was serving time for armed robbery.

Wandsworth prison officers were asked to guard against Ray's escape, suicide and assasination. Officers had to put the blade in Ray's razor before he shaved and remove it after he had finished shaving. Special care had to be taken to make sure he did not pick up any glass or other sharp object, and he was allowed to eat with only a melamine spoon.

Ray, who died in 1998 while serving a 99-year prison sentence for the assassination of the civil rights leader, initially confessed to the crime but later proclaimed his innocence, claiming it was a conspiracy. During his time in Wandsworth he made a number of references to killing, which were duly noted by prison officers who had to make a brief report after every shift spent guarding him.

"He said the assassination had been organised by one of his own lieutenants to gain control of the organisation funds," one officer noted.

"The assassination that has taken place in the USA [was] spoken of by him in association with the Black Muslim group. He implied they could be behind the Martin Luther King shooting," wrote another.

He told prison officers that his three weeks in London before his capture had not been enjoyable. "He said he did not like English food," an officer wrote. "He was in the habit of going out in the evening and purchasing half a chicken and a can of Heineken on the Cromwell Road."